Labeling machines that glue labels to containers are known. These labels are transferred to containers by a vacuum drum.
In some cases, a glued label is not properly removed from the vacuum drum or is not transferred to a container. Instead, it is left on the vacuum drum. This label can eventually become detached from the vacuum drum, possibly leading to uncontrolled fouling or to uncontrolled disturbances in downstream labeling operations.
A label can fail to be detached for many reasons. One reason is a malfunction of the labeling unit itself. But the most common reason is that there is no container present at the time the label presents itself for transfer. This occurs, for example, when there is a gap in the container stream.
A known solution was to provide a buffer or storage table in the container transport direction upstream of each labeling machine and to accumulate a supply of containers awaiting labeling during operation. This supply enabled the labeling machine to be continuously operated. The operating speed or throughput of the labeling machine was increased or decreased as the supply of containers on the buffer or storage table rose or fell respectively so as to ensure the uninterrupted operation of the labeling machine and to avoid the presence of gaps appearing in the container stream being fed to the labeling machine.
By using a buffer or storage table and monitoring the supply of containers on that table it was also in particular possible to react to larger, longer-lasting gaps in the container stream being fed to the buffer and storage table by controlling the labeling unit accordingly. For example, a long gap in the container stream can be dealt with by moving the gluing device, which is provided within the labeling unit, away from its working position, which is very close to the vacuum drum, to an idle position, which is at a greater distance away from the vacuum drum. This shifting of the gluing device reliably prevents the vacuum drum and labeling unit from being fouled by glue and/or by labels that have been glued but not transferred to containers.
In modern container treatment installations, the component machines are increasingly interlocked with one another in such a way that the containers are conveyed with accurate spacing by transport star-wheels from one container treatment machine to a subsequent container treatment machine. This precludes the use of a buffer. As a result, the known method for compensating for gaps in the container stream is no longer effective. Consequently, different container treatment machines can no longer react individually to variations in the container stream by varying their operating speeds.
With labeling machines in particular, the problem arises that they should still react in an appropriate way to gaps in the container stream, i.e. to missing containers. Particularly with container treatment plants that have a high throughput (number of treated containers per unit of time), for example container treatment plants that process more than 40,000 containers per hour, the time between two containers is less than 0.09 seconds. Even if it were theoretically possible to suppress the presenting of a label for a “missing” container within a very short time interval, it is simply not possible, because of its relatively high mass, to control the gluing device at the vacuum drum so that if the label is “missing”, no glue is applied to the vacuum drum and the vacuum drum is not fouled by glue as a result. For this reason it would be practicable, at least with brief interruptions in the container stream, to present labels even for containers that are not present at the vacuum drum so as to prevent glue being applied directly to the vacuum drum and fouling the vacuum drum, and even allowing for the risk of the labeling unit being fouled and further labeling operations being disrupted by labels not transferred to containers and falling from the vacuum drum.